Aluminum-base alloys



Patented July 27, 1937 PATENT OFFICE AL UMmUMmAsE ALLOYS i Joseph A. Nocls, In, Tarentum, Pa., assignor to i Aluminum Company of America, Pittsburg Pa., a corporation of Pennsylvania No, Drawing.

Application August 10, 1936, Serial No. 95,177

20 Claims. (Cl.14821.1)

. This invention relates generally to the heat treatable strong aluminum-base alloys containing copper, with or without the so-called'hardeners or hardening elements. manganese, chromium, zirconium, molybdenum, beryllium, boron,

and titanium. More, particularly the invention relates to aluminum -copper alloys containing silicon. One of the objects of the invention is to provide thermally treated articles of such alloys,

Q tainable by thermal. treatment.

possessing greater improvemen'tin one or another physical property than has heretofore been ob- Another object of the invention is to provide articles composed of alloys of the type indicated, with improvement particularly in the direction of yield strength in the artificially aged condition. Another object is to provide high hardness in articles'composed of such alloys. A further object is to provide alloy articles which will have improved resistance to' corrosion in the artificially aged condition. These and other objects I attain with these alloys by the addition thereto of a small amount of tin, not exceeding 0.1 per cent and preferably more than about 0.05 per cent. In fact, I have found beneficial results to be obtained with as little as 0.005 per cent. The

ments mentioned above, the rest of thealloy being aluminum.

In amounts of about 0.15 to-15.0 per cent, tin

has been known .as an alloying element which in aluminum-base .alloys containing copper increases the fiuidity and improves the machining and polishing characteristicsfof the alloy. Its use, however, has been generally discontinued, it having been learned, as investigators .have pointed out, that tin in the amounts heretofore used adversely affects the hot working characterthe art, I have discovered that certain small. amounts of tin are beneficial and desirable in' aluminum-copper alloys with or without one or istics of aluminum and aluminum-base alloys, diminishes the corrosion resistance ofv such mate rials, and, generally, serves no Iusefuliunction not more advantageously obtained with other allo ing elements- 1 Contrary to the accepted opinion and trend .of

more of the elements silicon, nickel, and zinc;

' any of which alloys may also contain one or-more of the hardeners manganese, chromium, boron,

- scopic size.

I to say, when the alloy is subjected to artificial aging (preferably but not necessarily after high temperature heat treatment), say at a temperature between about and 200C.

The benefits of my invention appear to be due to the response of a peculiar internal alloy structure to the artificial aging treatment. Aging phenomena in aluminum-base alloys are believed to be the result'of the precipitation of an alloying element from a solid solution thereof in aluminum which is super-saturated with respect thereto. The precipitation is submicroscopic or on the border line between submicroscopic and microscopic. By careful methods, however, it is possible to. prepare metal specimens which, under the action of an etching agent, reveal a structure indicative of the artificially aged condition of the metal;

For example, a'section of an artificially aged wrought aluminum alloy article composed of 4.0 per cent of copper without tin, etched with a mixture of hydrofluoric, hydrochloric and nitric 'acids, shows under a magnification of 500 diameters an aluminum matrix composed of contrasting grains having distinctly marked boundaries. 'Particles of the constituent CllAlz are seenscattered through the matrix but substantially none are found in the grain boundaries. Thesame alloy containing 0.05 per cent of tin shows after the same artificial aging only slight grain contrast, the grain boundaries are distinctly less sharp; and they contain multitudes ofsmall particles'of CuAlz. According to the theories of submicroscopic precipitation, the differences in structure noted in the tin-containing alloy indicate a more advanced stage of submicroscopic yond the submicroscopic to the microscopic stage. This is evidenced by the particles of 'CllAl: in the grain boundaries, resulting from precipitated in submicrocoalescence of particles '-The foregoing enhanced aging phenomenon which occurs in the above described aluminum alloys containing tin is particularly manifested in. such alloys by the development, under the be -described.

When tin in amounts of 0.005 to 0.1 per cent is present in aluminum alloys containing 2.0 to 12.0 per cent of copper and free from magnesium, a relatively short artificial aging treatment; will develop high hardness. Thus an aluminum alloy casting containing 11.78 per cent of copper and 0.05 per cent of tin, heat treated for 16 hours at 515 C. and aged for 15 hours at 0., had a Brinell hardness of 122. The same alloy without tin, similarly heat treated and aged, had a Brinell hardness of only 107. Similarly, and under the same treatment, an alloy containing about 4.0 per cent of copper, about 10.0 per cent of silicon, and about 0.04 per cent of tin, developed a Brinell hardness of 124, while a similar alloy not containing tin developed a Brinell hardness of only 106.

A further effect of the tin addition upon aging is particularly evidenced in certain specially valuable and preferred alloys. Under the influence of aging treatments, aluminum alloys containing 2.0 to 6.5 per cent of copper, 0.005 to 0.1 per cent of tin, and substantially free from magnesium, developed yield strengths which are on the order of 30 to 200 per cent greater than the yield strengths of similar alloys not containing tin. While the fundamental reasons for such increase in yield strength are obscure, the effect is very pronounced. For instance, a magnesium-free aluminum-base alloy containing 4.0 per cent of copper and 0.05 per cent of tin was heat treated at 510 C. for 20 minutes, quenched to room temperature, and artificially aged for 18 hours at 150 C. This alloy had a yield strength of 43,000 pounds per square inch. A similar alloy,- similarly treated but not containing tin, had a yield strength of only 20,200 pounds per square inch.

In addition to the effects described, my invention possesses another advantage. The artificial aging of aluminum-base alloys containing copper in substantial amount usually results in a decreased resistance of the alloy to corrosion, but I have found that when these alloys, especially those of the preferred copper content (2.0 to 6.5 per cent as stated above), contain tin in the amount prescribed by my invention this detrimental result is considerably lessened by the enhanced aging effect. In particular the artificially aged alloys show a marked decrease in propensity to undergo intercrystalline or intergranular corrosion, a type of corrosion which is more objectionable than the ordinary surface type because it is often not readily apparent and so is apt to escape observation until the corroded part or article fails as a result of the internal weakening.

The aluminum-base alloys which are improved by the enhanced aging induced therein by the addition of small amounts of tin are those containing 2.0 to 12.0 per cent of copper, with or without certain other alloying elements which I have found to be useful in modifying the general properties of the alloy without masking or destroying the beneficial properties above noted. Thus the aluminum-copper alloys may contain 0.1 to 3.0 per cent of a class of hardening elements which may be present, separately or together; each, however, not exceeding greatly the following limits: manganese 0.1 to 2.0 per cent, chromium 0.1 to 1.0 per cent, boron 0.1 to 0.5 per cent, molybdenum 0.1 to 1.0 per cent, zirconium 0.1 to 0.5 per cent, beryllium 0.1 to 2.0 per cent, and titanium 0.03 to 0.5 per cent.

1 have determined that magnesium is a harmful addition to the alloys above described in that its presence in substantial amounts destroys in large part the effects induced by the addition of small amounts of tin.

The preferred alloys are those in which one or all the above described properties are present to a marked extent, especially the yield strength. These alloys, as above noted, contain 2.0 to 6.5 per cent of copper and 0.005 to 0.1 per cent of tin, 0.05 to 0.1 per cent being preferred, and they are characterized in the artificially aged condition by a yield strength substantially higher than that of the same alloy devoid of tin. In their preferred form, these alloys may also contain 0.1 to 1.0 per cent, in total, of one or more of the hardening elements above mentioned. For making'castings of the preferred alloys that are to be used in the unworked condition the alloys may contain a total of 0.1 to 5.0 per cent of an element of the class consisting of zinc, nickel, and silicon. When two or all three of the elements zinc, nickel, and silicon are present,

the total should not exceed 5.0 per cent, the

lower limits being .nickel 0.05 per cent, zinc 0.05 per cent, and silicon 0.05 per cent. For making wrought articles, the same foregoing lower limits should be observed, but where two or all three of the named elements are present, the upper limits should be, nickel 1.0 per cent, silicon 3.0 per cent, and zinc 5.0 per cent. For rolling or forging, the total amount of these elements should not exceed 3.0 or 4.0 per cent, but if the alloy is to be extruded a total of about 9.0 per cent is permissible. In general, for making cast unworked articles the lower limits for each element, when used alone, should be, silicon 0.1 per cent, nickel 0.1 per cent, and zinc 0.1 per cent, and the upper limits should be, silicon 14.0

per cent, nickel 7.0 per cent, and zinc 14.0 per cent. Furthermore, if two or more of the elements are present in cast unworked articles, the lower limits should be, silicon 0.05 per cent, nickel 0.05 per cent, and zinc 0.05 per cent, the total amount of any two or more of the elements being 14.0 per cent, the total nickel content, however, not exceeding 7.0 per cent.

As specifically illustrating these alloys, an example of a wrought aluminum-base alloy without magnesium, containing about 4.4 per cent of copper, about 0.85 per cent of manganese, about 0.75 per cent of silicon, about 0.4 per cent of iron may be cited. Two alloys of this composition, with and without the addition of 0.05 per cent of tin, were heat treated at 520 C. for 15 minutes, quenched in water, and subjected for 18 hours to an aging treatment at 143 C. The tinfree alloy had a tensile strength of 58,700 pounds per square inch, a yield strength of 33,250 pounds per square inch, and an elongation of 16.8 per cent in two inches. The other alloy containing 0.05 per cent of tin had a tensile strength of 63,190 pounds per square inch, a yield strength of 46,250 pounds per square inch, and an elongation of 11.0 per centin two inches. Another wrought alloy composed of copper 4.1 per cent, silicon 1.0 per cent, tin 0.05 per cent, without magnesium, heat treated at 520 C. for 15 minutes, quenched, and artificially aged at C. for 12 hours, had a tensile strength of 60,580 pounds per square inch and a yield strength of 50,150 pounds per square inch. The effect of tin upon the yield strength and hardness of cast alloys is illustrated by the following examples. Aluminum-base alloys containing copper 4.0 per cent,

silicon 3.0 per cent; and copper 4.0 per cent, silicon 10.0 per. cent; ,with and without the addition of 0.05 per cent tin, were cast, heat treatedat 504 C. for 20 h'oursquenched in water, and aged at 154 C. for 16 hours. .The yield strength and hardness values of these alloys which .were ob tained are as follows: 2

Alloy composition Ymd Brine strength-Lbs. hardmss per Silicon 'rmw Percent Percent Percent 4.0 3. 0 20, 000 '92. 4 4.0 3.0v 0. 05 29.870 110.0 4.0 10.0 x 13.930 09.4 4.0 10.0 0.05 I 26, 020 110.0

The aging treatments and heat treatments to which .the above mentioned alloys are subjected. in order to develop their advantageousproper aluminum-copper alloyto temperatures of about 100 to 200 C. until the desired increase inproperties is obtained. The artificial aging in .the preferred practice of the invention is preceded by heat treatment, but the enhanced .aging effect herein described and its general results maybe developed to an advantageous extent by] the artificial aging alone.

The aluminum base alloys'herein described and I claimed are those containing at-.le ast 70.0 per cent of aluminum, which metal may contain impurities, such as amounts of iron up toabout 1.5 per cent and, likewise, small amountsfof silicon such as are known to .occur in virgin aluminum.

The enhanced aging herein described as :re-,

sulting from the addition of tin in the stated amount to magnesium-free aluminum alloys con-.

taining from 2.0 to' 12.0 per cent of copperisob-Z tained in bothcast and wrought'articles. '-In the case of castings of.-such alloys containing tin, I have found that heat treatment at elevated temperatures without artificial aging P 10 duces a higher ductility'than isobtainable by heat treatment of a casting or the same alloy without the tin.- This species'of tl' e invention I do not claim specifically herein but do so in my copending application Serial No. 606,755, filed April 21, 1932, and issued as United States'Letters Patent 2,022,686,-under date of December In the appended claims the term tensile property, or the like; is intended to include hardness as a propertywhich can be favorably affected by the enhancedartificial aging produced by my sale.

invention. Also within the-spirit of the appended claims the article may be an ingot or other body designed for iurthercasting or for working, or

it may be a cast orwrought. article which is suitable for immediate'use or sale or which may require some further operation to. fiti't :for use or Articles and methods involving aluminum-copper alloys containing nickel; zinc; silicon and nickel; silicon and zinc; nickel andzingand silicon, nickel and zinc; and aluminum copper al like alloy free from tin.,, v

' .2. In a method of making anarticle of alumiloys containing none of theelements silicon,

claimed in my copending applications Serial Nos.

95,178, 95,179, 95,180, 95,181, 95,182, 95,183 and 606,756, respectively. This application is a con- I claim:

nickel and zinc; are not claimed herein but are ,tinuation-in-part of my copending application Serial No. 606,756, filed'April 21, 1932.

- 1. In a method of making-an article of alu'minum alloy, forming an article of a magnesiumfree alloy containing copper 2.0 to 12.0 per cent;

I silicon 0.1 to.14.0 per cent, and tin 0.005-to 0.1 per 1 cent, the remainder being essentially aluminum;

and artificially aging the article whereby a tensile property of the alloy isimproved over that of a num alloy, forming-an article of a magnesiumfree alloy containing copper 2:0 to 6.5 per cent, silicon 0.1 to 5.0 percent, and tin 0.005 to 0.1 per;

cent, the remainder .being essentially aluminum;

and artificially aging the article, whereby a tensile property of the alloy is improved over that of a like alloy freefrom 0111.

, 3. In a method of 'makinganarticle o'faluminum alloy, forming an afrticle'of a magnesiumfree alloy containing copper 2.0 to 12,0]per cent; silicon 0.1m 14.0 per cent; tin 0.005 to 0.1 perv cent; and atleast one hardeningelement of the class consisting 'o'f'manganese0.1 toj-2.0 per cent,

chromium 0.1 to 1.0 per-cent',boron 0.1 to 015 per cent, molybdenum 0.1 to 1.0 per cen t, zirconium and titanium 0.03 to 0.5 per cent,'the total hardenin'gcontent being 0.1 to 3.0'per cent, and the remainder being essentially aluminum; and artificially aging the article whereby a tensile property of the alloy-is improved over thatof a likealloy free from tin.

4. In a method of making an article of alumi-.

num alloy, forming an article of a magnesiumfree alloy containing copper 2.0 to 12.0 per cent, silicon 0.1 to 14.0 per cent, and tin 0.005 to 0.1 per cent, the remainder being essentially aluminum; and artificially aging thearticle between about C, and 200 C. inclusive, whereby a tensile property of thealloy is improved over that of a like alloy freezfrom tin,

5. In a method of making an article of aluminum alloy, forming an article of a magnesiumlfree' alloy containing cop'per2L0 to 6.5 per cent, a silicon 0.1 15050 per cent,.andj,tin 0.005-t0 0.1 per 0.1 to 0.5 per cent, beryllium 0.1 to 2.0 percent, a

cent, the remainder being essentially aluminum;

v and artificially" aging the article between about 100 C. and'200 C. inclusive, whereby a tensile perty of the alloy is improved over that of a l alloy free from tin."

6. In a method of makinganarticle of aluminum alloy, forming an article of a magnesium jfree alloy containing copper 2.0 to 12.0 per cent;

silicon 0.1 to 14.0 percent; tin 0.005 to 0.1 per a 1 cent; and atleast one hardening element of the class consisting of manganese 0.1 to 2.0 percent,

chromium 0.1 to 1.0 percent, boron 0.1-to 0.5 per cent, molybdenum 0.1 to.1.0 per cent, zirconium 0.1to 0.5 per cent, beryllium 0.1 to 2.0 per cent,

and titanium 0.03 to 0.5 per.cent,'the total hardening content being 0.1 to 3.0 per cent, and the remainder being essentially aluminum; andartificially aging the article between about, 100C.

and 200 C. inclusive, whei-febya tensile property of the alloy isimproved-=over-that of. a like alloy free from'tin." J y 1 v 7. -In av method of making'an article of aluminum alloy, forming an article ofa magnesiumfree alloy containing copper 2.0 to 12.0 per cent, silicon 0.1 to 14.0 per cent, and tin 0.005 to 0.1 per cent, the remainder being essentially aluminum; heat treating the article between about 400 C. and the temperature of incipient fusion; and artificially aging the article between about C. and 200 C. inclusive, whereby a tensile property of the alloy is improved over that 'of a like alloy free from tin.

8. In a method ofmaking an article of aluminum alloy, forming an article of a magnesiumfree alloy containing copper 2.0 to 12.0 per cent, silicon 0.1 to 14.0 per cent, and tin 0.05 to 0.1 per cent, the remainder being essentially aluminum; heat treating the article between about 400 C. and the temperature of incipient fusion; and artificially aging the article between about 100 C. and 200 C. inclusive, whereby a tensile property of the alloy is improved over that of a like alloy free from tin.

9. In a method of making an article of aluminum alloy, forming an article of a magnesiumfree alloy containing copper 2.0 to 6.5 per cent, silicon 0.1 to 5.0 per cent, and tin 0.005 to 0.1 per cent, the remainder being essentially aluminum; heat treating the article between about 400 C. and the temperature of incipient fusion; and artificially aging the article between about 100 C. and 200 C, inclusive, whereby a tensile property of the alloy is improved over that of a like alloy free from tin.

10. In a method of making an article of aluminum alloy, forming an article of a magnesiumfree alloy containing copper 2.0 to 6.5 per cent, silicon 0.1 to 5.0 per cent, and tin 0.05 to 0.1 per cent, the remainder being essentially aluminum; heat treating the article between about 400 C. and the temperature of incipient fusion; and artificially aging the article between about 100 C. and 200 C. inclusive, whereby a tensile property of the alloy is improved over that of a like alloy free from tin.

11. In a method of making an article of alumi num alloy, forming an article of a magnesiumfree alloy containing copper 2.0 to 12.0 per cent; silicon 0.1 to 14.0 per cent; tin 0.005 to 0.1 per cent; and at least one hardening element of the class consisting of manganese 0.1 to 2.0 per cent, chromium 0.1 to 1.0 per cent, boron 0.1 to 0.5 per cent, molybdenum 0.1 to 1.0 per cent, zirconium 0.1 to 0.5 per cent, beryllium 0.1 to 2.0 per cent, and titanium 0.03 to 0.5 per cent, the total hardening content being 0.1 to 3.0 per cent, and the remainder being essentially aluminum; heat treating the article between about 400 C. and the temperature of incipient fusion; and artificially aging the article between about 100 C. and 200 C. inclusive, whereby a tensile property of the alloy is improved over that of a like alloy free from tin.

12. In a method of making an article of aluminum alloy, forming an article of a magnesiumfree alloy containing copper 2.0 to 6.5 per cent; silicon 0.1 to 5.0 per cent; tin 0.005 to 0.1 per cent; and at least one hardening element of the class consisting of manganese, chromium, boron, molybdenum, zirconium, beryllium, and titanium, the total hardening content being 0.1 to 3.0 per cent, and the remainder being essentially aluminum; heat treating the article between about 400 C. and the temperature of incipient fusion; and artificially aging the article between about 100 C. and 200 C. inclusive, whereby a tensile property of the alloy is improved over that of a. like alloy free from tin.

13. An article of artificially aged aluminum alloy free from magnesium and containing copper 2.0 to 12.0 per cent, silicon 0.1 to 14.0 per cent, and tin 0.005 to 0.1 per cent, the remainder being essentially aluminum.

'14. An article of artificially aged aluminum alloy free from magnesium and containing copper 2.0 to 12.0 per cent, silicon 0.1 to 14.0 per cent, and tin 0.005 to 0.1 per cent; and at least one element of. the class of hardeners composed of manganese, chromium, boron, molybdenum, zirconium, beryllium, and titanium, the total hardening content being 0.1 to 3.0 per cent, the rem nder of the alloy being essentially aluminum.

15. An article of artificially aged aluminum alloy free from magnesium and containing copper 2.0 to 6.5 percent, silicon 0.1 to 5.0 per cent, and tin 0.005 to 0.1 per cent, the remainder of the alloy being essentially aluminum.

16. An article of artificially aged aluminum alloy free from magnesium and containing copper 2.0 to 6.5 per cent, silicon 0.1 to 5.0 per cent, tin 0.005 to 0.1 per cent; and at least one element of the class of hardeners composed of manganese, chromium, boron, molybdenum, zirconium, beryllium, and titanium, the total hardening content being 0.1 to 3.0 per cent, the remainder of the alloy being essentially aluminum.

17. An article of thermally treated aluminum alloy free from magnesium and containing copper 2.0 to 12.0 per cent, silicon 0.1 to 14.0 per cent, and tin 0.005 to 0.1 per cent, the remainder being essentially aluminum; the alloy being characterized by a structure produced by heating the alloy to over 400 C. but below incipient fusion, cooling the alloy, and thereafter artificially aging the alloy.

18. An article of thermally treated aluminum alloy free from magnesium and containing copper 2.0 to 12.0 per cent, silicon 0.1 to 14.0 per cent, and tin 0.005 to 0.1 per cent; and at least one element of the class of hardeners composed of manganese, chromium, boron, molybdenum, zirconium, beryllium, and titanium, the total hardening content being 0.1 to 3.0 per cent, the remainder being essentially aluminum; the alloy being characterized by a structure produced by heating the alloy to over 400 C. but below incipient fusion, cooling the alloy, and thereafter artificially aging the alloy.

19. An article of thermally treated aluminum alloy free from magnesium and containing copper 2.0 to 6.5 per cent, silicon 0.1 to 5.0 per cent, and tin 0.005 to 0.1 per cent, the remainder being essentially aluminum; the alloy being characterized by a structure produced by heating the alloy to over 400 C. but below incipient fusion, cooling the alloy, and thereafter artificially aging the alloy.

20. An article of thermally treated aluminum alloy free from magnesium and containing copper 2.0 to 6.5 per cent, silicon 0.1 to 5.0 per cent, and tin 0.005 to 0.1 per cent; and at least one element of the class of hardeners composed of manganese, chromium, boron, molybdenum, zirconium, beryllium, and titanium, the total hardening content being 0.1 to 3.0 per cent, the remainder being essentially aluminum; the alloy being characterized by a structure produced by heating the alloy to over 400 C. but below incipient fusion, cooling the alloy, and thereafter artificially aging the alloy.

JQSEPH A. NOCK, JR. 

